The invention relates to a metallic substrate and to a method for manufacturing a metal-ceramic substrate.
Metal-ceramic substrates or ceramic substrates with metallizations are known in the art, particularly as circuit boards or substrates for electrical and electronic circuits or modules, especially for high-power circuits or modules.
Also known is the so-called active soldering method (DE 22 13 115; EP-A-153 618) for bonding metal layers or metal foils forming metallizations, in particular also of copper layers or copper foils, with the respective ceramic material. In this process, which is used especially for manufacturing a metal-ceramic substrate, a bond is produced at a temperature of ca. 800-1000° C. between a metal foil, for example copper foil, and a ceramic substrate, for example aluminum-nitride ceramic, using a hard solder, which in addition to a main component such as copper, silver and/or gold also contains an active metal. This active metal, which is at least one element of the group Hf, Ti, Zr, Nb, Ce, creates a bond between the solder and the ceramic through a chemical reaction, while the bond between the solder and the metal is a metallic hard solder bond.
Also known is a method for manufacturing metal ceramic substrates with an aluminum-nitride ceramic (A1N ceramic) base, which is characterized, for example, by higher thermal conductivity as compared with aluminum oxide ceramic (EP 0 480 030). The metallization or the copper foil forming said metallization is applied to the ceramic in this known method by means of active soldering using an active solder, which contains as the solder material copper and a further component, for example silver, and an active solder component, e.g. titanium. The disadvantage of this known method is that the active solder component forms an electrically conductive bond with the aluminum nitride, for example titanium nitride, so that the etching procedure required for patterning of the metallization has to be carried out in at least two steps, namely so that the patterning of the metallization for creating strip conductors, contact surfaces, etc. takes place in a first etching step and in a second, subsequent step the electrically conductive material formed between the strip conductors, contact surfaces, etc. as a result of chemical reactions of the active solder component with the aluminum nitride has to be removed by etching. The removal of this material or reaction product is possible only with very aggressive and highly concentrated etching agents, which have a high impact on the environment, in addition to very demanding production requirements.
It is an object of the invention is to present a metal ceramic substrate with an aluminum-nitride and/or silicon-nitride ceramic base or substrate that eliminates this disadvantage.